1. Field of the Invention
The present invention relates to a two-beam interferometer, which is applied to a Fourier transform infrared spectrophotometer (FTIR) or the like.
2. Description of the Background Art
A Michelson interferometer, which is formed by two plane mirrors and a beam splitter, is employed as a two-beam interferometer for a Fourier transform infrared spectrophotometer. One of the two plane mirrors is a fixed mirror, and the other one is a moving mirror, which is continuously slidable.
Such a two-beam interferometer is particularly sensitive to change in environmental temperature, vibration, and the like. To this end, a dynamic alignment method utilizing a laser beam is employed as one of means for stabilizing interference conditions. However, the dynamic alignment method tends to disadvantageously complicate an apparatus employed therefor.
In another method, a corner cube is employed in place of a mirror, as an optical system which is resistant against vibration. In a conventional two-beam interferometer, a moving mirror for a Michelson interferometer is formed by a corner cube, which is supported by a mechanical bearing and slid in the horizontal direction.
In another conventional two-beam interferometer, two corner cubes are mounted on metal support rods respectively to be obliquely opposite to each other in a plane, and reciprocatively rotated in the plane in the opposite state.
In the aforementioned two-beam interferometer using the mechanical bearing, the summits of the corner cube are varied with respect to an optical axis of incident light, to inevitably cause discrepancy of interference conditions.
In the system of rotating the two corner cubes in an opposite state, on the other hand, discrepancy of interference conditions is inevitably caused by assembling conditions for the moving portions.